Probing the interactions between bovine hemoglobin and three berberine saturated fatty acid salts by multi-spectral techniques, conductimetry and molecular docking.

The clinical application of berberine is limited by its poor bioavailability. To overcome this, berberine-saturated fatty acid salts have been developed, yet their interaction mechanism with hemoglobin, a key transport protein, remains unclear. This study aims to comprehensively investigate the interactions between bovine hemoglobin (BHb) and three berberine mid-chain saturated fatty acid salts ([BBR][FAs], specifically berberine caproate ([BBR][CAP]), berberine heptylate ([BBR][HEP]), berberine octanoate ([BBR][OCT])) by various experimental and molecular docking methodologies. UV-visible and fluorescence spectroscopic analyses demonstrate that [BBR][FAs] can bind to BHb with 1:1 stoichiometry and quench its fluorescence intensity through a static quenching mechanism. According to the evidence of synchronous fluorescence, three-dimensional fluorescence and FT-IR spectrometry, it was found that the microenvironment and secondary structure of BHb undergo alterations upon binding with [BBR][FAs]. Based on Förster resonance energy transfer analysis, the binding distance between [BBR][FAs] and BHb was determined to be within the range of 2.98 to 3.15 nm. This binding is associated with an increase in the esterase-like activity of BHb. The aggregation behavior of [BBR][FAs] in BHb aqueous solution was investigated from conductivity measurement. The critical aggregation concentration of [BBR][FAs] exhibited a positive correlation with increasing concentrations of BHb. Molecular docking data confirmed that the binding of [BBR][FAs] to BHb was principally mediated by hydrophobic interaction, hydrogen bonding and van der Waals force. Furthermore, this work systematically compared the chain length-dependent binding affinity between [BBR][FAs] and BHb, and observed the order of binding strength as: [BBR][CAP] ˂ [BBR][HEP] ˂ [BBR][OCT]. These findings provide quantitative structure-affinity relationship data.